Stephen McConnell wrote:
From the front page:
The Avalon Meta Model defines the functional structure of component types and services. A Type definition contains information about deployment and runtime dependencies together with information about the services that a component type can provide.
The following page describes the XML schema used to define a Type instance - http://avalon.apache.org/meta/meta/info/type/index.html
This is paralleled in the API documentation for the immutable Type class (org.apache.avalon.meta.info.Type). Keep in mind that the Type is simply an immutable class that exposes all of the descriptive features of a component (that's it).
Ok. So by defining a type I don't "create" a component, which means if I only define a type, I can't lookup up something?
Not directly.
A Type is a description of a component implementation. Based on information accessible from an instance of Type you know all about the structural and runtime dependencies that a instance of a corresponding component class will require.
Now, we could argue about the correct terms for months but the term "type" is imho misleading here. If a type exposes all features of a component why is it called a type and not component?
What is a component?
Here is my view.
A component is a reusable computation unit that provides zero or more functional services. This implies that a component is more than a class or collection of classes. It is computational unit that can be deployed predictably in different application scenarios and environments.
To achieve this you can break down "component" into:
* a component *type* description * an *implementation* of the type * a deployment *profile*
Collectively these different aspect are brought together by a container through the process of "instantiating a component".
Stephen.
Carsten
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